The disclosure of Japanese Patent Application No. 2000-192509 filed on Jun. 27, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a traction control apparatus of a vehicle. More particularly, the invention relates to a braking force control type traction control apparatus and method.
2. Description of Related Art
In a known braking force control type traction control apparatus of a vehicle, such as a motor vehicle or the like, described in, for example, Japanese Patent Application Laid-Open No. HEI 5-229414, a vehicle speed, i.e., vehicle body speed, is detected, and the traction control is prohibited when the vehicle speed is in an intermediate-to-high speed range.
Since this traction control apparatus prohibits application of braking force to drive wheels in an intermediate-to-high vehicle speed range where the vehicle traveling inertia is great, the apparatus prevents early wear-out of brake pads and any damage to the engine caused by application of sharply increased loads to the brake mechanism and the drive system by the traction control.
In general, the revolution inertia of the engine increases with increases in the engine revolution speed. Therefore, the adverse effect caused on the engine and the drive system by sudden application of braking forces to the drive wheels by the traction control increases with increases in the engine revolution speed. However, the engine revolution speed does not necessarily increase with increases in the vehicle speed.
The aforementioned conventional traction control apparatus is designed so that the traction control is prohibited when the vehicle speed is in a relatively high speed range. Therefore, although the conventional traction control apparatus is able to prevent the occurrence of an excessively great load on the breaking mechanism when the vehicle traveling inertia is great, and braking force is applied to the drive wheels, the conventional traction control apparatus is not able to effectively and reliably reduce the adverse effect of the traction control on the engine and the drive system.
Furthermore, due to the aforementioned design of the conventional traction control apparatus in which the traction control is prohibited when the vehicle speed is in a relatively high speed range as mentioned above, there is another problem that can occur when using the conventional apparatus. That is, if drive slip occurs when the vehicle speed is relatively high, the conventional traction control apparatus is not able to apply braking force to the drive wheels at all, so that the drive slip cannot be reduced.
Accordingly, it is an object of the invention to effectively and reliably prevent the adverse effect of the traction control on the engine and/or the drive system, and reduce the drive slip by controlling the increasing rate of braking force applied to drive wheels in accordance with the engine revolution speed.
In accordance with a first mode of the invention, a traction control apparatus and method of a vehicle for reducing a drive slip of a drive wheel by applying a braking force to the drive wheel includes detecting an engine inertia force, and reducing a rate of increasing the braking force during a traction control if the engine inertia force is high, compared with a case where the engine inertia force is low.
According to the above-described mode, if the engine inertia is high, e.g., if the engine revolution speed or the engine-generated torque is high, the braking force increasing rate during the traction control is reduced, in comparison with a case where the engine inertia force is low, e.g., if the engine revolution speed or the engine generated torque is low. Therefore, the adverse effect caused by application of a sharply increased load to the engine and/or the drive system during the traction control is effectively and reliably reduced. Furthermore, when the engine inertia force is great, the braking force applied to the drive wheels is not reduced, but the braking force gradually increases to a needed value. Therefore, the drive slip is effectively and reliably reduced, in comparison with a case where when the engine inertia force is great the traction control apparatus is prohibited or the braking force is reduced.
In the above-described mode, a controller may reduce the rate of increasing the braking force during the traction control if the braking force applied to the drive wheel is high, compared with a case where the braking force applied to the drive wheel is low.
Thus, when the braking force applied to the drive wheel is great, the braking force increasing rate during the traction control is reduced, compared with the increasing rate in a case where the braking force is small. Therefore, the adverse effect caused by application of a sharply increased load to the engine and/or the drive system during the traction control can be more effectively and reliably reduced than in the above-described first mode.
In the above-described mode, the controller can detect a speed reduction ratio of a transmission apparatus, and increase an amount of reduction of the rate of increasing the braking force during the traction control when the speed reduction ratio is great, compared with a case where the speed reduction ratio is small.
In general, even if the engine revolution speed is fixed, the adverse effect caused on the engine and the drive system by application of braking force to the drive wheel is greater in the case of a great speed reduction ratio of the transmission than in the case of a small speed reduction ratio. Accordingly, the amount of reduction of the braking force increasing rate during the traction control is made greater in the case of a great speed reduction ratio of the transmission than in the case of a small speed reduction ratio. Therefore, the adverse effect caused by application of a sharply increased load to the engine and/or the drive system during the traction control can be more effectively and reliably reduced, in comparison with a case where the speed reduction ratio of the transmission is not taken into consideration.
In the above-described mode, the controller may reduce the rate of increasing the braking force during the traction control, by reducing an upper limit of the rate of increasing the braking force.
Therefore, the braking force increasing rate during the traction control is reduced by reducing the upper limit of the braking force increasing rate. Hence, the increasing rate of the braking force applied to the drive wheel during the traction control can be reliably reduced.
In the above-described mode, the controller may reduce the rate of increasing the braking force during the traction control so that the rate of increasing the braking force decreases with increases in the engine revolution speed.
Furthermore, the braking force increasing rate-reducing device may reduce the rate of increasing the braking force during the traction control so that the rate of increasing the braking force decreases with increases in the braking force applied to the drive wheel.
The braking force applied to the drive wheel may be estimated based on the rate of increasing the braking force, and on a control time based on the rate of increasing the braking force.
Furthermore, the controller may increase the amount of reduction of the rate of increasing the braking force during the traction control with increases in the speed reduction ratio of the transmission apparatus.
Still further, the controller may set the upper limit of the rate of increasing the braking force, in accordance with an engine revolution speed and the drive force applied to the drive wheel.
The controller may also correct the upper limit of the rate of increasing the braking force, in accordance with the speed reduction ratio of the transmission apparatus.